1. Field of Technology
Embodiments disclosed herein relate generally to switching power converters, and more specifically, to techniques for estimating input current indirectly from the peak value of the primary side current of switching power converters.
2. Description of the Related Arts
In switching power converters, the input current is often sensed and/or controlled to provide high power factor. Power factor in switching power converters is defined as the ratio of the real power delivered to the load to the apparent power provided by the power source. Utility companies or government agencies require power factors in switching power converters to exceed a certain minimum level by regulation. Thus, switching power converters should deliver power from the power source to the load with a high power factor and low total harmonic distortion. To achieve high power factor and low total harmonic distortion, the input current of a power converter is regulated to follow the input voltage as closely as possible.
Furthermore, the input current is often sensed and/or controlled to ensure correct operation of dimmer switches in light emitting diode (LED) lamp system applications. LED lamp systems generally include a LED lamp used with a dimmer switch. Conventional dimmer switches adjust lamp input voltage using a TRIAC circuit. A TRIAC is a bidirectional device that conducts current in either direction when it is triggered (i.e., turned on). Once triggered, the TRIAC continues to conduct until the current drops below a certain threshold, called a holding current threshold. For the internal timing of a TRIAC dimmer to function properly, a minimum input current must be maintained in order to keep the dimmer on. Thus, the input current of the power supply needs to be sensed in order for a controller of the power supply to control the power supply to provide enough current to the dimmer to keep the dimmer on while minimizing power loss through the power supply.
In conventional power converters, the input current is sensed directly by a sensing resistor or a current sense transformer. However, the direct measurement of the input current requires extra components which increase the system bill of material cost as well as the size of the system. Also, directly sensing the input current causes additional power loses through the components used to directly sense the input current.